1. Field of the Invention
This invention relates to a packaging material for photosensitive materials, and more particularly, this invention relates to a packaging material suitable for the photographic photosensitive materials having sharp edges and a heavy weight, such as sheet films not having round corners including lithfilm and cut film, roll film and rolled photographic printing paper.
2. Description of the Prior Art
As the laminated films for photosensitive materials of which physical strength have been improved, the present inventor has already disclosed various packaging materials. For example, the packaging material illustrated in FIG. 17 is composed of an aluminum foil layer 9a and two uniaxially stretched high density polyethylene (HDPE) resin films 10a laminated on both sides of the aluminum foil layer each through a low density polyethylene (LDPE) resin extrusion adhesive layer 5' so that their molecular orientation axes cross each other (U.S. Pat. No. 4,331,725). Another packaging material for weight photosensitive materials is composed of a foamed sheet and two uniaxially stretched films laminated on both sides thereof so that their molecular orientation axes cross each other (U.S. Pat. No. 4,565,733).
Moreover, as regards the packaging material using linear low density polyethylene (L-LDPE) resin, the inventor has disclosed a light-shielding film of which properties are improved by blending a light-shielding material (U.S. Pat. No. 4,452,846).
Before these packaging materials have been developed, the double sheet gusset bag combining the inner sheet shown in FIG. 16 and an outer sheet having three layer composition was used for packaging photographic photosensitive materials requiring the strongest physical strength. The inner sheet is composed of a light-shielding LDPE resin film layer 8a, a metal foil layer 9 laminated thereon through an adhesive layer 5', a flexible sheet layer 4 laminated thereon through an adhesive layer 5' and another light-shielding LDPE resin film layer 8a further laminated thereon through an adhesive layer 5'.
The tear strength of the packaging material disclosed in U.S. Pat. No. 4,331,725 is remarkably improved. However, when the packaging material is made into a single sheet bag having little buffer action, such as the light-shielding moistureproof bag for packaging a rolled photographic photosensitive material, it became liable to be broken by the sharp edge of the roll. Moreover, the single sheet bag had a problem in heat seal strength and other heat seal properties, such as sealability in low temperature and pinhole formation. The equipment cost including molding machine for the production of uniaxially stretched film was expensive, and generation of cutting loss was also great. Therefore, this packaging material was expensive. The packaging material of FIG. 16 was used as the inner sheet of a conventional double sheet gusset bag, and combined with the outer sheet composed of Clupak paper and a light-shielding LDPE resin film layer laminated thereon through a LDPE resin adhesive layer. However, the double sheet gusset bag was also broken by the sharp edge of a photographic photosensitive material. The packaging material disclosed in U.S. Pat. No. 4,565,733 had buffer action, and it was excellent in physical strength. However, its bag-making ability particularly for automatic bag-making machine was inferior. Generation of the cutting loss of uniaxially stretched film was great, and the packaging material was expensive. This packaging material was difficult to be put to practical use other than the packaging bag substitute for metal can and the packaging bag for a bulk roll in view of processibility and cost.